Insulin has profound effects on a number of diverse cellular processes. It produces these "immediate" and "delayed" effects subsequent to its interaction with a specific receptor on the cell membrane. The coupling mechanism(s) between the insulin-receptor interaction and the subsequent metabolic effects produced by insulin action remains unclear. We are studying the coupling mechanisms by exploiting our recent findings that (i) insulin action on fat cells increases the phosphorylation of ATP-citrate lyase: (ii) this increase in enzyme phosphorylation is not mediated by cylic AMP-dependent protein kinase (cAMPdPK) in vivo: and (iii) structural site phosphorylation is hormone dependent. Recent evidence from our laboratory demonstrated that the site phosphorylated by ATP-citrate lyase kinase was different from that phosphorylated by the catalytic subunit of cAMPdPK. In addition, recent evidence from our laboratory has demonstrated that acetyl CoA carboxylase is an excellent substrate for phosphorylation by ATP-citrate lyase kinase (cAMPiPK). Our general hypothesis is that insulin action increases a cAMPiPK (?lyase kinase) activity which increases the phosphorylation of structural phosphates of ATP-citrate lyase and of other key molecules such as acetyl-CoA carboxylase. The crux of this proposal is to study whether ATP-citrate lyase kinase, a cyclic AMP independent protein kinase (cAMPiPK) is competent to, in a physiological way, phosphorylate a key enzyme in fatty acid biosynthesis acetyl-CoA carboxylase. If ATP-citrate lyase kinase or another cAMPiPK can phosphorylate acetyl-CoA carboxylase at a specific site (in vivo insulin specific site) separate from those sites which are phosphorylated under the control of cAMPdPK, as preliminary evidence suggests, then that cAMPiPK becomes a candidate to be an insulin dependent protein kinase. Not only will this study define a proximal step in the mechanism of insulin action, i.e. activation of an insulin d PK, but will describe in a more meaningful way how insulin action controls fatty acid biosynthesis by regulating specific site phosphorylations.